has vetoed a bill requiring public employee unions to obtain annual authorization before members’ union dues can be automatically deducted from paychecks.

The bill — SB 29 — also required authorization before the dues could be used for political purposes. Republicans have long sought both provisions.

But Nixon said the bill was unfair to public employees.

“Public employees who are members of unions would be required to complete two separate authorizations each year,” Nixon’s veto message says. “Singling out union dues for these extra processes serves no beneficial purpose.”

Republicans are expected to object. They’ll have an opportunity to override in September.

The bill exempted public safety officials from the requirements. Nixon said that violates equal protection requirements in the Constitution.